Remodeling of gap junctions promotes ventricular tachycardia in patients with healed infarcts, but much less is known about the role of altered coupling in arrhythmogenesis in patients with cardiac hypertrophy and failure. The proposed research is designed to elucidate mechanisms of altered coupling at gap junctions in response to increased load leading to myocardial hypertrophy. Using a novel, custom-designed apparatus to subject neonatal rat ventricular myocytes to defined mechanical stress in vitro, we have demonstrated that expression of Cx43, the major gap junction protein in the heart, is up-regulated by >2-fold in cultured myocytes after only 1 hr of pulsatile stretch, leading to a significant increase in conduction velocity. In Specific Aim 1, we will determine whether static stretch also up-regulates Cx43 expression, characterize the reversibility of these changes, and determine whether imposition of a greater load down-regulates Cx43, analogous to what occurs during the transition to heart failure. In Specific Aim 2, we will define the relative contributions of changes in Cx43 protein synthesis and degradation to the up-regulation of Cx43 expression induced by pulsatile stretch. In Specific Aim 3, we will test the hypothesis that pulsatile stretch stimulates release of VEGF, which acts in an autocrine manner to activate signaling pathways leading to enhanced Cx43 expression. The results of the proposed studies will provide insights into mechanisms responsible for altered electrical coupling and conduction during the development of hypertrophic growth.